Diagnostic Laboratory Section

ANALYSIS OF MICROBIAL LOAD IN WATER

Materials

• 250 ml sterilized bottles, water bath, Double strength MacConkey broth, Nutrient agar, and MacConkey agar.

Qualitative analysis

• Take 100 ml of sample and inoculate into equal amount of the double strength MacConkey broth, incubate the samples at 37°C for 24 hrs. After 24 hrs incubation, observe for acid and gas production in the samples, If it positive reaction indicates presence of non-faecal Coliform.
• If the Incubator temp is 41 °C, and there is production of acid and gas after 24 hrs in the samples it indicates presence of Faecal Coliform.

Quantitative method

• Take 25ul of water sample and inoculate onto the Petri plates containing pre poured Nutrient Agar, MacConkey Agar and incubate the plates at 37 °C for 24 hrs in the incubator.

Observation

• Count the number of colonies. The total count should be not more than 10 colonies. Coliform count should be nil

Action to be taken 

• In case presence of Coliform in the water, take immediate action for cleaning with disinfectants such as Hydrogen Peroxide or Bleaching powder.